Why do recruiters ask are you involved in any other interviews?

What is it with recruiters from recruitment agencies when they ask if you are involved in other interviews at the moment or not?

She asked me this question and then asked do you mind me telling which companies you are interviewing with? And I was dumb enough to name 3-4 which I am having interviews with. Now thinking that not only I am competing against 100 other candidates for those positions but also the new resumes she will submit there. To clarify I got all of these interviews myself without any help from a recruitment agency and yes If it’s destined for me I will get the job but just frustrated so wanted to vent.